mtv wrote:
Apparently you haven't been around Cubs much. Those things been holing the tails on airplanes for a whole lot longer than you've been on this earth.

MTV

Jeese Mike, lighten up

I have been around cubs, and many other Piper tails as an A&P and an Inspector, I was just asking for a little explanation. Also, I had a good feeling Zane was not planning on using those clevis in that specific wire-pull application.

Hard to go wrong with the spherical bearing rod end, they work well in the elevator trim system on the Beaver.

Damn, and I thought this spread was about CLEAVAGE

Zane, personally I'm going to go with the ball ends on my Patrol. Much tighter linkage, on a surface that you definitely don't any slop or resulting flutter on.
But I honestly never thought about an electric trim. Probably lighter and faster to build than a cable operated one. May have to look into it now.

I was just nosing around my hangar renter's Rans S-12 and saw this:



That's the el grande version being used on a brake pedal.

Then I was snooping around a familiar S-7 and saw the pushrod ends that Courierguy was alluding to:



Pretty snazzy. I like the tapered inserts.

Then, my brain hiccuped when I saw his electric trim:



That's the servo right there mounted on the elevator. That must have been what you were referring to, Papa Foxtrot?

Back to stamped cleavage: I think they're a bombproof component. Super simple. I'm not sure what the argument could be against them, even for flight controls. I still need a good way to attach to the rod end spherical coming off the servo output shaft.

Phil, I've grown to really like electric trim on the stick. No need to remove your hand and you can adjust on short final without a thought.

Bear_Builder wrote:Zane, personally I'm going to go with the ball ends on my Patrol. Much tighter linkage, on a surface that you definitely don't any slop or resulting flutter on.
But I honestly never thought about an electric trim. Probably lighter and faster to build than a cable operated one. May have to look into it now.

Sorry Phil - that comment's not quite right - ball ends are the 'sloppiest' part of the BH's controls at the stick, and trim uses them too. I would design them out if I were you.

I did what Z is going to do, and there is zero slop in that system from the servo to the drive.

I do have some 'sloppiness' in the through-bolts attachments out at the tabs themselves. Those linkages under the tail flop around something fierce and it's loosened the bolted joints right out. I think this has come about by using bolts that were too short (done to get the drilled hole in the right place) and the threads have eaten away at the eyes.I have to live with that now, until there's enough room for a sacrificial bushing.

Zzz wrote:...I've grown to really like electric trim on the stick. No need to remove your hand and you can adjust on short final without a thought.

+1. I got spoiled by Beechcraft. It's REALLY nice.

I design them in with spherical ends. The extra cost involved is justified for me a lot of times because of adjustabity and reduction of fastener count. The adjustability is gained by using LH and RH threads and jambs. The self lube units do not last as long ...radial play goes up faster than one might think.

Zzz wrote:Back to stamped cleavage: I think they're a bombproof component. Super simple. I'm not sure what the argument could be against them, even for flight controls. I still need a good way to attach to the rod end spherical coming off the servo output shaft.

Phil, I've grown to really like electric trim on the stick. No need to remove your hand and you can adjust on short final without a thought.

The only thing I can think of, given those parts are stamped - is the residual stress in the bends - that will increase their propensity to crack if there's a scratch on their surface and they have an applied cyclic stress i.e. flying wires / tailwings.

Electric trim on the stick +1
I had second thoughts during the build, but I am loving it for bush flying - no need to stop what you're doing to trim.

Another guy is doing a dual electric / manual trim on his BH, using a capstan servo with a clutch, on the trim control wires. Great solution, best of both worlds - just slightly heavier (his is an IFR Bear).

Spherical ends are what I am using in the stick steering system I'm installing on the boat I'm working on. I chose them over stamped clevis ends because I don't want any slop and I don't want to pull the floor boards to service anything. Clevis ends are great in a push only or pull only setup but for a push/pull system spherical ends are the way to go, IMO.

That pushrod end on the S7 would be a nice way to to attach the spherical from the servo to the pushrod and would give you the finish you desire.

Zzz wrote:Then, my brain hiccuped when I saw his electric trim:



That's the servo right there mounted on the elevator. That must have been what you were referring to, Papa Foxtrot?

Yep - that looks like the standard Ray Allen pushrod. I'm building the Bearhawk LSA; which only has the trim tab on one side. The elevator is too thin to mount the servo there, but I've thought about mounting it in the horizontal stab. I'll likely put it in the tail section though - better protection from weather and also in the unlikely event that I decide to go back to a cable system later.

Watch the weight though. The best advice I've received is take care of the ounces and the pounds will take care of themselves!

In the excavation world we use tenths not inches to measure.
Inches are for carpenters and hookers.

We also use a shackle not a clevis.
Farmers use a clevis.

Not sure about airplanes, but growing up in the logging industry "clevis" is just not an acceptable word.

Terry wrote:In the excavation world we use tenths not inches to measure.
Inches are for carpenters and hookers.

We also use a shackle not a clevis.
Farmers use a clevis.

Not sure about airplanes, but growing up in the logging industry "clevis" is just not an acceptable word.

I think it's probably good that your airplane was built in a factory.

Zzz you might want to talk to Russ Erb about all the fun he had with his trim tab on a Bearhawk. You can find him through the EAA Chapter 1000 website.

It's not that there is a lot of load on the trim tab, there probably isn't much under normal conditions. But a tiny little microscopic movement over and over again will cause a failure just as much as a single overload. The use of a clevis that has any movement, or deformation could make something brittle over time, which could crack, which make your trim tab come loose, which could give you the same experience Russ had.

But you guys are missing something important... those thin wall style clevises used on tail wires are only loaded in tension when they are used on the tail of a Cub, as MTV mentioned. The load is constant as well as one-way. There is no "push-pull" loading.

If you are using threaded rod with nuts, in a push-pull servo installation, this is a different ball game. Stop and think why they saw fit to make thick wall clevises for push-pull control systems. Those engineers were not amateurs, and they took safety very seriously. Experimental or not, that is always a good position to take.

The thicker wall clevises that you show in the very first picture looks a lot better than the thin wall ones to me. But there are gen-u-wine degreed engineers on this forum who have far more engineering knowledge than I... if one of them says that the thin wall clevis will be safe over time and thousands of push-pull loadings, then take their word over mine.

Although not catastrophic, I've had two flutter incidents in my time as a racer, and I can promise it is not something you want to take lightly.

http://www.aircraftspruce.com/catalog/a ... kkey=68834

Lots of certified planes use this for what you are doing.

Haha. I think I have what I need. Thanks everyone.

EZFlap wrote:Zzz you might want to talk to Russ Erb about all the fun he had with his trim tab on a Bearhawk. You can find him through the EAA Chapter 1000 website.

It's not that there is a lot of load on the trim tab, there probably isn't much under normal conditions. But a tiny little microscopic movement over and over again will cause a failure just as much as a single overload. The use of a clevis that has any movement, or deformation could make something brittle over time, which could crack, which make your trim tab come loose, which could give you the same experience Russ had.

But you guys are missing something important... those thin wall style clevises used on tail wires are only loaded in tension when they are used on the tail of a Cub, as MTV mentioned. The load is constant as well as one-way. There is no "push-pull" loading.

If you are using threaded rod with nuts, in a push-pull servo installation, this is a different ball game. Stop and think why they saw fit to make thick wall clevises for push-pull control systems. Those engineers were not amateurs, and they took safety very seriously. Experimental or not, that is always a good position to take.

The thicker wall clevises that you show in the very first picture looks a lot better than the thin wall ones to me. But there are gen-u-wine degreed engineers on this forum who have far more engineering knowledge than I... if one of them says that the thin wall clevis will be safe over time and thousands of push-pull loadings, then take their word over mine.

Although not catastrophic, I've had two flutter incidents in my time as a racer, and I can promise it is not something you want to take lightly.

Bill, an excellent clarifying post.

Any of the ideas listed will work fine.

It is good to note the differences in the load conditions (reversing stress vs unaxial), but seriously, an off the shelf 1/16" thick 1045 fork tang, annealed after forming, under completely reversed bending, is less than half the way to the endurance S-N curve with a 50-lb reversed load. Pretty much *anything* will probably meet the requirement for a trim tab.

Except, perhaps, shoelaces.

The more important consideration is likely the lash if one is worried about flutter. The collision will move the stress from well below the endurance limit to well over it very quickly. Given the number of homebuilts that have used one or all of the above methods, I'm betting that the lash issue is one that is addressed with any of them adequately.